This computer is still based on the PDP-8 architecture but is less "opened" than the DECmate II. Indeed DEC realised that the PDP-8 based products were rarely expanded to their full potential. Thus, they conceived the DECmate III wich offers less expansion possibilities but which was also cheaper.
As the last incarnation of the PDP-8 technology, the DECmate III use a single chip containing all the PDP-8 hardware !

Only one pair of 5''1/4 disk-drives (RX50) is supported and it is not possible to connect a Hard-Drive. But unlike the DECmate II, a color monitor can replace the monochrom screen.

It was mainly intended for professionnal word-processing, but could also run other software including OS/278. The DECmate III was compatible with the DECmate II.

In 1985, a DECmate III+ was sold with a hard disk controller built-in and overall completely new hardware components, though still compatible with the DECmate II and III.